This present invention relates to coating compositions which have an improved pot life without a corresponding increase in dry time.
Two-component coating compositions containing, as binder, a polyisocyanate component in combination with an isocyanate-reactive component, in particular a polyhydroxyl component, are known. They are suitable for the formation of high quality coatings and can be adjusted to produce coatings which are hard, elastic, abrasion resistant, solvent resistant and especially weather resistant. A disadvantage of these systems is the amount of organic solvent which must be used to reduce the viscosity of these systems for subsequent processing.
This disadvantage may be overcome according to copending application, U.S. Ser. No. 07/540,536, filed Jun. 19, 1990, allowed Jun. 30, 1992 as U.S. Pat. No. 5,126,170, which is directed to coating compositions wherein the binders are based on a two-component system of a polyisocyanate component and an isocyanate-reactive component containing partly or entirely certain secondary polyamines. The copending application discloses that the coating compositions provide numerous advantages. For example, they are suitable in particular as binders in low solvent or solvent-free coating compositions and enable the coatings to harden rapidly by a chemical cross-linking reaction which takes place either at room temperature or elevated temperature.
A disadvantage of the coating compositions described in the copending application is that even though they possess fast dry times, for some applications they do not provide adequate pot life, i.e., the viscosity of the system increases too rapidly prior to application of the coating compositions to a substrate.
Accordingly, it is an object of the present invention to provide a longer pot life without significantly increasing the dry time of the coating composition and without altering any of the other desirable properties of the composition.
Surprisingly, this object may be achieved with the coating compositions of the present invention which contain certain tin compounds to be described hereinafter. It is surprising that an increase in the pot life can be obtained by incorporating these tin compounds because they are generally regarded as catalysts for polyisocyanate polyaddition reactions and, thus, would be expected to shorten the pot life of the coating compositions.